Guide element for a tubular film

ABSTRACT

A guide element for a tubular film which is produced by blown film extrusion. The guide element includes a support structure having guides secured to the support structure and acting upon the circumference of the tubular film. The support structure includes a plurality of support limbs that are articulated to each other and that are received so as to be adjustable relative to each other by adjusting drives. At least one guide for the tubular film is secured to each support limb.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a guide element for a tubular film manufactured by the blown film extrusion process, having a support structure with guides that are fastened to the support structure and that act on the circumference of the tubular film.

2. Discussion of Related Art

In the manufacture of plastic films by the so-called blown film extrusion process, the melted mass of thermoplastic plastic manufactured by at least one extruder is extruded from an annular exit opening of a die and blown into a tube, which is then folded by a so-called flattening device into a double-layered film web, conveyed between squeezing rollers, and then supplied to a winding device.

In the simplest case, the flattening device is of two flattening elements, which are arranged in diametrically opposite regions of the tubular film and are adjustable at an acute angle in relation to each other, similar to an inverted V or an A, and whose distance from each other, when viewed in the exit direction of the tubular film, continuously decreases. The flattening elements have a number of guides such as strips, rollers, or brushes, which act on the circumference of the tubular film so that the tubular film, which is initially cylindrical, is gradually flattened, passing through an oval shape with continuously changing diameters, into the form of a double-layered film that is folded at its longitudinal edges.

If the oval cross-sectional shape of the gradually flattened tubular film, which shape takes form starting from the initially cylindrical tubular film, is viewed in the flattening device, then the tubular film, in the region of the larger diameter of the oval cross section at which the folded longitudinal edges of the tubular film finally forms, is largely left alone during the flattening because it is not in contact with the guides and is not guided by the flattening elements of the flattening device. This can lead to problems with regard to product stability, freedom from wrinkles, and the like.

U.S. Pat. No. 4,170,624 discloses transforming an initially cylindrical tubular film into a rectangular cross section in a special flattening device and then flattening it into a double layer. The intent of this is to avoid mechanical stress on the tubular film during the flattening and resulting changes in the properties profile of the tubular film.

It is thus desirable to also provide a definite lateral guidance of the tubular film, such as in the regions not guided by the flattening elements. Because of the straight arrangement of the brushes, rollers, or strips used as guides for the tubular film, though, which has up to now been the default arrangement in the prior art, it is only possible to provide an insufficient point-by-point contact. Particularly in reversing movements of the flattening device and/or a withdrawal device for the tubular film, which is situated after the squeezing rollers, the film starts to form slight wrinkles that run all the way through the completed roll and reduce the quality. This situation is clearly in need of improvement.

SUMMARY OF THE INVENTION

In order to solve this problem, this invention proposes guide elements whose support structure has a plurality of support legs, which are connected to one another in articulating fashion and are secured so that they can be adjusted in relation to one another by adjusting drive units, and at least one guide means for the tubular film is fastened to each support leg.

These guide elements can be used both as flattening elements and as lateral guide elements.

The guide elements according to this invention can be adjusted in various ways and can be individually adapted to the circumferential curvature of the tubular film passing through the flattening device.

In particular, the guide elements according to this invention can be used as lateral guide elements in a lateral guide device having two lateral guide elements, which are arranged in diametrically opposite regions of the tubular film, between the flattening elements, and each has a guide element according to this invention.

A flattening device according to this invention has two flattening elements, which are arranged in diametrically opposite regions of the tubular film and are adjustable at an acute angle in relation to each other, for transforming the initially circular cross section of the tubular film, passing through oval cross sections, into a double-layered film web, and has lateral guide elements, which are situated between the flattening elements, are associated with the tubular film, and are for the regions of the tubular film untouched by the flattening elements.

According to one embodiment of this invention, each support leg of the guide element according to this invention has a separate adjusting drive unit in order to achieve the most flexible possible adjustment options.

The guide means can be fastened to the support legs in a rigid or an articulating manner by at least one support arm.

The guide means can be rollers or drums of a suitable plastic such as CFK, silicone, or also aluminum. It is also possible to provide roller brushes or to provide plates from which a current of air emerges in order to produce an air cushion between the plate and the tubular film to ensure a contact-free guidance. Preferably, the plates have a microporous surface in order to produce a homogeneous air cushion. The term “microporous” is understood here to refer to an average pore diameter of 5 to 100 μm. In the case of rotating rollers or drums, it is preferable to ensure a particularly smooth running.

The support structure of the guide element according to this invention is of a plurality of support legs, which are connected to one another in articulating fashion and can be individually adjusted by suitable adjusting drive units in accordance with the desired path of the tubular film as it passes through the flattening device. In this case, one or more support arms for holding the guide means can be fastened to each support leg. At least one support arm is provided for each support leg.

Other adjusting possibilities can be provided by securing the guide means to the support arms, in a manner that allows them to pivot around a pivot axis extending in the exit direction of the tubular film.

The adjustment of the support legs, which are connected to one another in an articulating fashion and extend from one another in a segmented fashion, because of the separate adjusting drive units provided for the support legs, can be embodied in various ways with respect to the angle enclosed between adjacent support legs in order to adapt to the changing cross section of the tubular film. According to another embodiment of this invention, it is possible for the individual support legs to be longitudinally adjustable, for example by a suitable telescoping mechanism, which offers additional degrees of freedom for adapting to the desired contour of the tubular film to be flattened. Also, an adjustment transverse to the longitudinal span of the support legs can permit an adaptation to different diameters of the tubular film.

Embodying the guide element according to this invention with a large number of support legs, such as at least three support legs, also makes it possible to emulate arc-shaped desired contours of the tubular film with a high degree of approximation, particularly if the support arms fastened to the individual support legs and the holding forks, which are for the guide means and are fastened to these arms, are adjustable, for example vertically adjustable, laterally adjustable, and angularly adjustable.

According to another embodiment of this invention, each guide element, at the upper end region of the support structure, can have a guide blade, and when the guide element according to this invention is used in a lateral guide device, comes to rest close to the squeezing rollers of the extrusion device and encloses the outside of the longitudinal edge that forms during the flattening of the tubular film, and guides the forming edge fold until it travels into the roller nip between the squeezing rollers, and thus ensures an exact embodiment of the edge fold of the flattened tubular film. This guide blade can also be produced from suitable plastics or also aluminum, for example, if it comes into contact with the tubular film or can also be equipped with a porous, preferably microporous, surface oriented toward the tubular film to permit a supplied current of air to emerge and to produce an air cushion for a contact-free guidance of the tubular film.

Also in this connection, a microporous surface is understood to be a surface with an average pore size of 5 to 100 μm.

The distance of the guide blades to the subsequent squeezing rollers should be selected to be small and is preferably adjustable, thus preferably permitting a definite guidance of the longitudinal edge of the tubular film all the way into the roller nip of the squeezing rollers.

The adjustment of the individual support legs can, for example, be executed with a high degree of positioning precision by spindle drive units or other suitable drive units. It is also preferable for each support leg to have a separate adjusting drive unit. The adjusting drive units can also be centrally connected to one another.

BRIEF DESCRIPTION OF THE DRAWINGS

Other embodiments and details of this invention are explained in view of an exemplary embodiment shown in the drawings, wherein:

FIG. 1 is a schematic side view of a guide element according to one embodiment of this invention;

FIG. 2 shows a cross-sectional shape of a tubular film that changes as the tubular film is flattened; and

FIG. 3 is a view of a part of a guide element embodied according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of a tubular film 1, which is manufactured in a known manner, guided vertically upward in an exit direction A out of an extrusion device, and gradually folded into a flat tubular film by flattening elements, not shown in detail, of a flattening device. The drawing also shows a lateral guide device that is part of the flattening device and is equipped with a lateral guide element 2, which is also provided on the opposite side, symmetrical to the central longitudinal axis of the tubular film 1.

Through the action of the flattening elements, which according to the depiction in FIG. 2, engage a region labeled with the reference numeral 300 of the initially cylindrical tubular film 1, such as with a circular cross section Q1, the tubular film 1 is gradually transformed, passing through oval cross sections that are labeled Q2 and Q3, by way of example, into a flattened double-layered film web with a cross section Q4 and edge folds 10.

During this flattening process from the cross section Q1 to the cross section Q4, the lateral guide elements 2 guide the tubular film 1 continuously in the region 400 of the larger diameter, such as between the flattening elements labeled with the reference numeral 300.

Each lateral guide element 2 comprises, according to FIG. 1, a support structure with three support legs labeled with the reference numerals 20, 21, 22, which are connected to one another, such as in a chain, by articulating joints 23, 24.

Each of the support legs 20, 21, 22 supports support arms 25 to which are secured guides or guide means 27 for the tubular film 1, which are oriented toward the tubular film 1, are embodied in the form of CFK rollers, for example, and contact the surface of the tubular film 1, guiding it precisely in the desired contour.

As shown in FIG. 3, the free end of each support arm 25 can have pairs of guide means 27 that are supported, if necessary, in an articulating fashion by a pivot axis S extending in the entry direction of the tubular film 1 in order to adapt optimally to the circumference of the tubular film 1.

In lieu of guide means in the form of rollers, the upper support segment 20, viewed in the exit direction A, has a guide blade 27 a that grasps the outside of the edge fold 10, which forms during the flattening of the tubular film 1, and ensures a precise guidance of it all the way to the nip between the squeezing rollers 5, which are positioned or situated congruently one behind the other in FIG. 1.

Because of the articulating connection between the individual support legs 20, 21, 22, it is possible to adjust them relative to one another with respect to the enclosed angle in order to adapt to the desired contour of the tubular film. For this purpose, independent drive units such as spindle drive units 28 are provided, which in the exemplary embodiment shown, engage the support leg 20 and the support leg 22 while the support leg 21 positioned between them has a cantilever 29 that is engaged by the drive unit 28. The drawing also shows an additional engaging arm of a drive unit 28 a, which directly engages the cantilever 29. With this configuration and through actuation of the individual drive units 28, 28 a, it is possible within broad boundaries to adjust the angular orientation of the succeeding support arms and thus of the guide means for the tubular film 1 that are fastened to them and in particular, it is possible to optimally reproduce the arc-shaped edge curvatures that form on the tubular film 1 to be flattened and thus to achieve a significantly more precise guidance that results in a significantly improved quality of the flattened tubular film 1.

Alternatively, it is also possible to provide a separate drive unit 28 for each support leg 20, 21, 22, without connecting these drive units to one another.

The support legs 20, 21, 22 can be adjusted independently of each other in the direction of the diameter D of the tubular film and can also each telescope in the arrow direction T, for example are embodied as longitudinally adjustable, so that their axial length can be adapted or changed.

In lieu of the three support legs 20, 21, 22 shown here, it is also possible to provide only two such support legs or more than three support legs and to provide them with corresponding drive units. In another embodiment, each support leg has at least one support arm 25 for a guide means.

The guide elements according to this invention can be used not only as a lateral guide element 2, but also as a flattening element of the flattening device. 

1. A guide element for a tubular film (1) manufactured by a blown film extrusion process, comprising a support structure with guide means (27) fastened to the support structure and that act on a circumference of the tubular film, the support structure having a plurality of support legs (20, 21, 22) connected to one another in articulating manner and adjustably secured relative to one another by adjusting drive units (28, 28 a), and at least one guide means (27) for the tubular film (1) fastened to each one of the support legs (20, 21, 22).
 2. The device as recited in claim 1, wherein each of the support legs (20, 21, 22) has a separate adjusting drive unit (28, 28 a).
 3. The device as recited in claim 2, wherein the guide means (27) are fastened to the support legs (20, 21, 22) by at least one support arm (25).
 4. The device as recited in claim 3, wherein the guide means (27) are of rollers, drums, brush rollers, or plates on which a current of air can act to produce an air cushion.
 5. The device as recited in claim 4, wherein an angle is adjustable between succeeding support legs (20, 21, 22) and/or an axial length is adjustable of the support legs (20, 21, 22), and/or a position is adjustable of the support legs transverse to the longitudinal span.
 6. The device as recited in claim 5, wherein a guide blade (27 a) is provided at an upper end of the support structure.
 7. The device as recited in claim 6, wherein it is possible to lay the guide blade (27 a) against the tubular film 1 or, with the guide blade (27 a), to produce an air cushion for a contact-free guidance of the tubular film (1).
 8. A flattening device for a tubular film (1) manufactured by a blown film extrusion process, comprising two flattening elements situated in diametrically opposite regions of the tubular film (1) and adjustable at an acute angle in relation to each other to transform an initially circular cross section of the tubular film (1), passing through oval cross sections, into a double-layered film web, and having lateral guide elements (2) situated between the flattening elements, associated with the tubular film (1), and for regions of the tubular film (1) left free by the flattening elements.
 9. The device as recited in claim 1, wherein the guide means (27) are fastened to the support legs (20, 21, 22) by at least one support arm (25).
 10. The device as recited in claim 1, wherein the guide means (27) are of rollers, drums, brush rollers, or plates on which a current of air can act to produce an air cushion.
 11. The device as recited in claim 1, wherein an angle is adjustable between succeeding support legs (20, 21, 22) and/or an axial length is adjustable of the support legs (20, 21, 22), and/or a position is adjustable of the support legs transverse to the longitudinal span.
 12. The device as recited in claim 1, wherein a guide blade (27 a) is provided at an upper end of the support structure.
 13. The device as recited in claim 12, wherein it is possible to lay the guide blade (27 a) against the tubular film 1 or, with the guide blade (27 a), to produce an air cushion for a contact-free guidance of the tubular film (1). 